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RESEARCH PAPERS

# Formation Damage Issues Impacting the Productivity of Low Permeability, Low Initial Water Saturation Gas Producing Formations

[+] Author and Article Information
D. Brant Bennion

Hycal Energy Research Laboratories Ltd. ( a division of Weatherford International)

F. Brent Thomas

Hycal Energy Research Laboratories Ltd. ( a division of Weatherford International)

J. Energy Resour. Technol 127(3), 240-247 (Apr 21, 2005) (8 pages) doi:10.1115/1.1937420 History: Received August 10, 2004; Revised April 20, 2005; Accepted April 21, 2005

## Abstract

Very low in situ permeability gas reservoirs $(Kgas<0.1mD)$ are very common and represent a major portion of the current exploitation market for unconventional gas production. Many of these reservoirs exist regionally in Canada and the United States and also on a worldwide basis. A considerable fraction of these formations appear to exist in a state of noncapillary equilibrium (abnormally low initial water saturation given the pore geometry and capillary pressure characteristics of the rock). These reservoirs have many unique challenges associated with the drilling and completion practices required in order to obtain economic production rates. Formation damage mechanisms affecting these very low permeability gas reservoirs, with a particular emphasis on relative permeability and capillary pressure effects (phase trapping) will be discussed in this article. Examples of reservoirs prone to these types of problems will be reviewed, and techniques which can be used to minimize the impact of formation damage on the productivity of tight gas reservoirs of this type will be presented.

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## Figures

Figure 1

Pore scale illustration of how increasing water saturation reduces effective flow area and permeability to gas

Figure 2

Typical low permeability gas-water∕oil relative permeability curves

Figure 3

Mechanism of water blocking in a low permeability gas reservoir

Figure 4

Illustration of porous media dominated by macro porosity and how this can reduce phase trapping potential

Figure 5

Illustration of porous media dominated by micro porosity and how this can reduce phase trapping potential

Figure 6

Results from a typical laboratory scale phase trap test using a water based completion fluid for a low permeability gas reservoir

Figure 7

Typical water-gas capillary pressure curves for a low permeability gas reservoir

Figure 8

Typical hydrocarbon based phase trap mechanism in a low permeability gas reservoir

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